[[interceptors]]
= Wiring Spring Beans into Producer/Consumer Interceptors

Apache Kafka provides a mechanism to add interceptors to producers and consumers.
These objects are managed by Kafka, not Spring, and so normal Spring dependency injection won't work for wiring in dependent Spring Beans.
However, you can manually wire in those dependencies using the interceptor `config()` method.
The following Spring Boot application shows how to do this by overriding Spring Boot's default factories to add some dependent bean into the configuration properties.

[source, java]
----
@SpringBootApplication
public class Application {

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

    @Bean
    public ConsumerFactory<?, ?> kafkaConsumerFactory(SomeBean someBean) {
        Map<String, Object> consumerProperties = new HashMap<>();
        // consumerProperties.put(..., ...)
        // ...
        consumerProperties.put(ConsumerConfig.INTERCEPTOR_CLASSES_CONFIG, MyConsumerInterceptor.class.getName());
        consumerProperties.put("some.bean", someBean);
        return new DefaultKafkaConsumerFactory<>(consumerProperties);
    }

    @Bean
    public ProducerFactory<?, ?> kafkaProducerFactory(SomeBean someBean) {
        Map<String, Object> producerProperties = new HashMap<>();
        // producerProperties.put(..., ...)
        // ...
        Map<String, Object> producerProperties = properties.buildProducerProperties();
        producerProperties.put(ProducerConfig.INTERCEPTOR_CLASSES_CONFIG, MyProducerInterceptor.class.getName());
        producerProperties.put("some.bean", someBean);
        DefaultKafkaProducerFactory<?, ?> factory = new DefaultKafkaProducerFactory<>(producerProperties);
        return factory;
    }

    @Bean
    public SomeBean someBean() {
        return new SomeBean();
    }

    @KafkaListener(id = "kgk897", topics = "kgh897")
    public void listen(String in) {
        System.out.println("Received " + in);
    }

    @Bean
    public ApplicationRunner runner(KafkaTemplate<String, String> template) {
        return args -> template.send("kgh897", "test");
    }

    @Bean
    public NewTopic kRequests() {
        return TopicBuilder.name("kgh897")
            .partitions(1)
            .replicas(1)
            .build();
    }

}
----

[source, java]
----
public class SomeBean {

    public void someMethod(String what) {
        System.out.println(what + " in my foo bean");
    }

}
----
[source, java]
----
public class MyProducerInterceptor implements ProducerInterceptor<String, String> {

    private SomeBean bean;

    @Override
    public void configure(Map<String, ?> configs) {
        this.bean = (SomeBean) configs.get("some.bean");
    }

    @Override
    public ProducerRecord<String, String> onSend(ProducerRecord<String, String> record) {
        this.bean.someMethod("producer interceptor");
        return record;
    }

    @Override
    public void onAcknowledgement(RecordMetadata metadata, Exception exception) {
    }

    @Override
    public void close() {
    }

}
----
[source, java]
----
public class MyConsumerInterceptor implements ConsumerInterceptor<String, String> {

    private SomeBean bean;

    @Override
    public void configure(Map<String, ?> configs) {
        this.bean = (SomeBean) configs.get("some.bean");
    }

    @Override
    public ConsumerRecords<String, String> onConsume(ConsumerRecords<String, String> records) {
        this.bean.someMethod("consumer interceptor");
        return records;
    }

    @Override
    public void onCommit(Map<TopicPartition, OffsetAndMetadata> offsets) {
    }

    @Override
    public void close() {
    }

}
----

Result:

[source]
----
producer interceptor in my foo bean
consumer interceptor in my foo bean
Received test
----

